Problem: Expand. If necessary, combine like terms. $(7+x)(7-x)=$
Notice that this expression has the following special form: $(a+b)(a-b)$ This form expands to what we call "a difference of squares": $( a+ b)( a- b)= a^2- b^2$ Using the above pattern, we get: $\begin{aligned} ( 7+ x)( 7- x)&= 7^2- x^2 \\\\ &=49-x^2 \end{aligned}$